The invention concerns a process and an accompanying mechanism for the direction-selective triggering of a passive safety device in a vehicle, particularly relevant to an airbag system when the vehicle is involved in a crash. It has at least two acceleration transducers with directional sensitive axes and these sensitive axes are aligned in different directions. It also has an evaluation device which picks up the signals from the acceleration transducers, processes them and makes output signals available to trigger the passive safety device.
The invention also concerns a process to determine factors.
Process and mechanism for the direction-selective triggering of a passive safety device in a vehicle are familiar, for example, from DE 37 17 427, DE 37 33 837 C2 or DE 41 16 336 C1.
Nowadays, practically all new cars are equipped with airbags to provide passive protection for the occupants of the vehicle. In the event of a crash, the airbags are inflated very quickly by gas, protecting the passengers sitting behind them from the consequences of a crash or at least considerably reducing the amount of damage caused by the accident.
The optimum trigger time for airbags is amongst other things, a function of the angle at which the vehicle collides with an obstruction or an oncoming vehicle. This can usually be taken into account in trigger units for airbags or in other passive safety devices, such as seatbelt constraint systems, by two acceleration transducers. But when the acceleration transducers are manufactured, when the acceleration transducers are mounted on a board, when the board is fitted into equipment housing and when the equipment is installed in the vehicle, angle tolerances distort the accuracy of the angle information, making it impossible to achieve the optimum triggering instant.
In principle, the direction sensitivity of acceleration sensitive elements such as piezoelectric components, is generally really good. However, the uncertainty in the measurement result generally comes from inaccuracies during installation of the acceleration sensitive elements in the acceleration transducer housing, the acceleration transducer on the board, the board in the housing and the finished unit in the vehicle. Distortion of a signal working in the acceleration transducer's direction of maximum sensitivity, is less to blame for the error in measurement. It is more a case of the greatest distortion being experienced by those signal components which are applied perpendicularly. In the data sheets, this value is usually called cross sensitivity, but in almost all cases, it is nothing more than the angle of torsion, at which the acceleration sensitive element can be installed, compared to the nominal angle of its directional sensitive axis.
It would be extremely expensive to manufacture acceleration transducers with a sufficiently low angle tolerance and to install them accurately enough in the unit and in the vehicle. That is why the familiar mechanisms are either expensive to manufacture, because components with particularly precise angle sensitivity have to be used, or expensive to install and therefore more expensive, because if less precise components are used, once they are installed, sensitivity has to be equalized with great accuracy and the angle tolerance offset.